As males become physically masculinized, the male body is characterized by the buildup of skeletal muscle, the maturation of the genital organ, the growth of spermatogenic tissue in the testicles, and sexual inclination; all of which are backed by testosterone, with the concomitant occurrence of dihydrotestosterone-mediated negative conditions including the generation of acne, enlargement of sebaceous glands, alopecia, and benign prostatic hyperplasia. Hair loss, mostly found in men, has long been studied, but the causes of hair loss and growth have yet to be proven. There is increasingly an imperative need for the prevention and treatment of hair loss because hair has greater social significance for people in many aspects, including aesthetics in modern society.
Hair is an organism that follows a specific growth cycle with three phases of anagen, catagen and telogen. Strands of hair independently experience growth cycle phases, so that the number of hair is kept nearly constant. The number of hairs on any individual is actually determined at birth. In many cases, the maturation of hairs by sex hormones is mistaken for an increase in the number of hairs.
The anagen phase is known as the growth phase, during which the cells in the papilla actively divide to produce new hair fibers, and the follicle buries itself into the dermal layer of the skin to nourish the strand. The anagen phase lasts about 2˜6 years. About 85% of the hairs on one's head are in the anagen phase at any given time. Around the papilla is the hair matrix, a collection of epithelial cells in the form of a bulb. In the anagen phase, these cells are constantly dividing, adding to the hair shaft. The catagen phase is a short transition phase in which the follicle rapidly shrinks, with its growth activity stopped. This phase lasts for about 2˜3 weeks while club hair is formed. The catagen phase accounts for about 5% of the hairs on one's head in a given time. The telogen phase is the resting phase in which the cellular activity of the hair follicle remain dormant. It lasts about 2˜3 months, during which the preceding club hair is pushed up and out by the new, growing strand or normally lost by mechanical actions, for example, by combing or washing one's head. Generally, alopecia is the term for the abnormal loss of hair which results from a reduction in the proportion of the hair in the anagen phase to that in the catagen or telogen phase.
Alopecia is caused by various factors including the action of male sex hormones, mental stress, the accumulation of lipid peroxide, side-effects from drugs or radiotherapy, chronic diseases such as leukemia and tuberculosis, malnutrition, etc. Recently, hair loss, which has been regarded as a male ailment, is now frequently found in women and the youth, with increasing demand for the prevention and treatment of hair loss.
Among medications for use in promoting hair growth, or as hair tonics, there are now vasodilators for promoting the circulation of sufficient blood to the scalp, female hormones for suppressing the action of male hormones, and male hormone inhibitors for suppressing the activity of 5α-reductase which converts testosterone into 5-DHT (5-dihydrotesteone). Examples of the vasodilators include carpronium chloride, minoxidil and various plant extracts. Within the range of the useful female hormones are estrogen, estradiol and progesterone. The male hormone inhibitors are exemplified by finateride and pentadecanoic acid.